18th Annual CBE Graduate Student Research Symposium

Computational modeling of materials can be a powerful complement to experimental methods when models with useful levels of predictive ability can be deployed more rapidly than experiments. Achieving this goal involves judicious choices about the level of modeling that is used and the key physical properties of the materials of interest that control performance in practical applications. I will discuss two examples of using high throughput computations to identify new materials for scalable energy applications: the use of metal-organic frameworks in membranes and gas storage and the selection of metal hydrides for high temperature nuclear applications. These examples highlight the challenges of generating sufficiently comprehensive material libraries and the potential advantages and difficulties of using computational methods to examine large libraries of materials.

David Sholl is the School Chair of Chemical & Biomolecular Engineering at Georgia Tech, where he is also the Michael E. Tennenbaum Family Chair and GRA Eminent Scholar in Energy Sustainability. David’s research uses computational materials modeling to accelerate development of new materials for energy-related applications, including generation and storage of gaseous and liquid fuels and carbon dioxide mitigation. He has published over 260 peerreviewed papers. He has also written a textbook on Density Functional Theory, a quantum chemistry method that is widely applied through the physical sciences and engineering. David is a Senior Editor of the ACS journal Langmuir. More information on David’s research group is available from www.chbe.gatech.edu/sholl

Yersiniabactin (Ybt) is a mixed nonribosomal peptide-polyketide natural product natively produced by the pathogen Yersinia pestis. The compound enables iron scavenging capabilities upon host infection and is biosynthesized by a nonribosomal peptide synthetase featuring a polyketide synthase module. This pathway has been engineered for expression and biosynthesis using Escherichia coli as a heterologous host. The biosynthetic process for Ybt formation has been improved through the incorporation of a dedicated step to eliminate the need for exogenous precursor provision. Furthermore, precursor-directed biosynthesis was used to systematically produce Ybt analogs. Upon doing so, resulting compounds were tested in applications that highlight the metal chelating nature of the compound. More specifically, the compounds are being tested for industrial wastewater heavy metal removal and recovery with the goal of aiding the environmental and economic outcomes associated with processes across the electrical, plating, semiconductor, solar panel, automotive, and e-waste sectors

Crystallinity is an important property of macromolecules (polymers) of synthetic or natural origin as it affects profoundly material properties such as mechanical, optical, and barrier. The presence of crystalline domains hinders the dissolution of semicrystalline polymers and thus constrains their subsequent physical and/or chemical processing. Cellulose is a prime example of a semicrystalline polymer the recalcitrance of which to most solvents prevents the efficient conversion of the abundant and renewable cellulosic biomass toward high-value-added products. Despite research efforts, many aspects of semicrystalline polymer dissolution such as solvent-induced decrystallization and polymer chain untangling are not well-understood.

Our research is addressing these fundamental issues with the practical goal of gaining insights into the swelling and dissolution of cellulose that support the preparation of cellulose-based functional polymers and nanomaterials. To this end, we have developed a phenomenological model that captures the transport phenomena governing the dissolution of semicrystalline polymers, e.g., solvent penetration, transformation from crystalline to amorphous domains, specimen swelling, and polymer chain untangling, as well as the thermodynamics and kinetics of dissolution.

This model fits well experimental data for swelling and dissolution of cotton fibers in the ionic liquid [Bmim]Cl, and allows the quantification of two important features, i.e., effectiveness of solvent (i) in cellulose decrystallization and (ii) in untangling cellulose chains, the balance of which controls the mechanism and kinetics of cellulose dissolution. The insights obtained from this study facilitate the design of efficient solvent systems and processing conditions for the dissolution of cellulose and other semicrystalline polymers.